As wireless data transmission becomes more common and the need for capacity increases, the changing capacity requirements can be met by enhancing the use of the existing infrastructure of telecommunications systems. One way of increasing the capacity of a wireless telecommunications system is to utilize data transmission modes in the data transmission between a base station and a user terminal that are more advanced than the existing data transmission modes.
One way of enhancing the capacity of a wireless telecommunications system is to utilize various diversity modes, such as time diversity and antenna diversity, in data transmission between a base station and a user terminal. In the case of antenna diversity, the radio interface is implemented so that the same signal is received and/or transmitted using antenna elements which have different locations and polarizations. This way the probability increases that at least one antenna element is located in an advantageous place in respect of the signal path. Use of antenna diversity requires an antenna solution where the distance between antenna elements is sufficiently long so that one can keep the interference between the electromagnetic waves related to the antenna elements low and provide a large number of alternative signal paths between the base station and the user terminal. A base station utilizing antenna diversity functions in ‘antenna diversity mode’.
Another way of increasing the capacity of a wireless telecommunications system is to use beam forming. In beam forming, the signal power of a base station can be directed to the areas that need capacity. In addition, a signal directed to different areas can be encoded in a beam-specific manner. Beam forming requires an antenna solution where the distance between antenna elements is sufficiently short to enable unequivocal beam forming and to avoid grating lobes. A base station utilizing beam forming functions in ‘beamforming mode’.
In a prior art solution the antenna arrays of a base station allow the base station to function either in antenna diversity mode or in beam-forming mode.
A problem associated with the prior art solution is that the base station is unable to support simultaneously both the antenna diversity mode and the beam-forming mode. Switching of the data transmission mode between the above-mentioned modes requires modification of the whole antenna arrangement or replacement of the whole old antenna arrangement with a new one. This results in significant disadvantages to the operation of the radio system.